δ-tocotrienol Induces GGCX Expression and Inhibits HepG2 Cell Proliferation

Des-gamma-carboxy-prothrombin (DCP) is an autologous growth factor as well as a well-known tumor marker of hepatocellular carcinoma. DCP is converted to prothrombin by γ-glutamyl carboxylase (GGCX), the expression of which is low in hepatocellular cancer (HCC) tissue. An alternatively spliced variant of GGCX, lacking exon 2, shows expression patterns correlating with DCP level in specific HCC cell lines such as HepG2. In order to seek for chemical compounds that may correct the exon 2 skipping of GGCX, we tested three well-known splicemodulating compounds that induce exon-inclusion: kinetin; EGCG; and δ-tocotrienol. Among the three, δ-tocotrienol decreased cell viability of HepG2 cells in MTS assays. By RT-PCR and Western blot analyses, δ-tocotrienol induced GGCX mRNA expression strongly at 3 μM that was inhibited by sulforaphane but with no effect on alternative splicing. Though δ-tocotrienol did not significantly affect DCP production, it had a strong effect on HepG2 cell viability, evidenced by PARP cleavage and scratch assays